The present invention relates in general to motors for actuating air conditioners, industrial machines, electric vehicles, etc., and, more particularly, the invention relates to the structure of a motor having a rotor inside which permanent magnets are set so that reluctance torque as well as magnetic torque is utilized.
A high efficiency motor which utilizes reluctance torque as well as magnetic torque by setting permanent magnets inside a rotor core, viz., so called xe2x80x9can interior permanent magnet motorxe2x80x9d is already known. FIG. 9 is a cross sectional view showing the rotor of such conventional motor. In FIG. 9, the rotor is shaped into a cylinder having substantially the same shaft as that of a stator (not illustrated) and is supported by a bearing (not illustrated) for rotating on a shaft 76. The rotor has eight permanent magnet slits 73 inside a rotor 71, and these slits are disposed, along the rotating direction of the rotor, at the intervals of substantially same spacing and are extended through the core along the direction of the shaft. To the slits 73, an adhesive is applied, then plate shaped permanent magnets 72 are inserted, and the magnets 72 are stuck to the rotor core 71. With this structure, the rotor has eight magnetic poles.
The rotor is disposed inside the stator leaving a narrow annular clearance, then it is rotated by the attracting and repulsing force of the magnetic poles of the rotor to the stator teeth which have rotating magnetic fields created by the electric current which runs through the windings of the stator.
In the above structure, the relation between the inductance xe2x80x9cLdxe2x80x9d of a d-shaft direction which meets at right angles with the magnetic poles of the rotor and the inductance xe2x80x9cLqxe2x80x9d of a q-shaft direction which runs through the border between adjacent rotor magnetic poles is expressed as Lq greater than Ld.
Generally, the relation between a motor torque xe2x80x9cTxe2x80x9d and the parameters of the number of rotor magnetic pole pairs xe2x80x9cPnxe2x80x9d, an interlinkage flux xe2x80x9cMaxe2x80x9d, a stator winding current xe2x80x9cIxe2x80x9d, an advanced phase angle (electrical angle) xe2x80x9cbxe2x80x9d of the current xe2x80x9cIxe2x80x9d to the induced voltage generated in each phase stator winding by the winding current xe2x80x9cIxe2x80x9d is expressed as,
T=Pn{Maxc2x7Ixc2x7cos(b)+0.5(Lqxe2x88x92Ld)I2xc2x7sin(2b)}
In the above equation, the first term represents a magnetic torque and the second term represents a reluctance torque. In the above described structure, Lq greater than Ld, so that by controlling to advance the phase of the winding current xe2x80x9cIxe2x80x9d to the phase of the induced voltage generated in each phase winding, thereby xe2x80x9cbxe2x80x9d becomes positive, then the reluctance torque is generated. By setting xe2x80x9cbxe2x80x9d at a predetermined value, the torque xe2x80x9cTxe2x80x9d can be made larger comparing that of only magnetic torque with the same electric current.
In the above described conventional structure, the rotor has the permanent magnet slits 73 in the rotor core 71, then the adhesive is applied to the walls of the slits 73, then the permanent magnets 72 are stuck inside the slits 73. Then, if the clearances between the slits 73 and the magnets 72 are large, the positions of the magnets 72 become unstable, then the magnetic flux disperses and the characteristic of the motor is deteriorated.
In addition, the big clearances cause the use of thick layers of the adhesive, whereby the effective magnetic flux decreases, which results in a decrease in the torque. Namely, if there are thick adhesive layers between the outer rotor rim 75 and the magnets 72, the magnetic resistance increases between them, so that the magnetic flux, which is produced by magnets 72 and runs into the stator, decreases, then the magnetic torque decreases and the output power of the motor also decreases.
Therefore, stabilization of the positions of the magnets 73 is tried by decreasing the clearances between the slits 73 and the magnets 72 by adjusting the section size of the magnets 72 and that of the inserting openings of the slits 73 to be substantially the same.
However, if the clearances between the walls of the slits 73 and the magnets 72 are small, the insertion of the magnets 72 is difficult and also the adhesive applied to the walls of the slits 73 is pressed out when the magnets 72 are inserted into the slits 73. Accordingly, the adhesive layers between the walls of the slits 73 and the magnets 72 mostly disappear, causing concern as to whether the magnets 72 are firmly stuck inside the slits or not. Also, if the adhesive layers are not thick enough, the motor may loose reliability on the problem of the dropping out of the magnets 72 at high speed rotation.
The rotor of xe2x80x9cthe interior permanent magnet motorxe2x80x9d is driven not only by the magnetic torque, which directly contributes for generating the torque by the magnetic flux which is produced by magnets 72 and runs into the stator, but also the motor is driven by utilizing the reluctance torques which is generated by the above described difference between the inductance xe2x80x9cLdxe2x80x9d and the inductance xe2x80x9cLqxe2x80x9d. While if the space of the outer rotor rim 75 between the magnets 72 and the outer rim edge of the rotor core 71 is narrow, the magnetic flux path becomes also narrow, then the magnetic saturation occurs, and the volume of the magnetic flux which runs there decreases and the reluctance torque becomes small.
It has been suggested to dispose the magnets 72 at positions closer to a shaft 76 for taking wider space of the outer rotor rim 75, and then for making a larger magnetic flux path so that the magnetic flux runs well and that the large reluctance torque is utilized. However, in that case, the ends of the magnets 72 are more separated from the outer rim edge of the rotor core 71, then the magnetic flux runs into the adjacent magnets, and the effective volume of the magnetic flux for generating the torque decreases.
While, the structure for preventing the pressing out of the adhesive when permanent magnets are stuck to the rotor of a motor is stated in the Japanese Patent Application Unexamined Publication No. H08-251850. The rotor, as illustrated in FIG. 10, has a groove 84 for absorbing the excess of an adhesive 88 applied to a portion where a cylindrical permanent magnet 82 is stuck to a shaft 86. In the illustration, the thickness of the adhesive layer 88 is enlarged.
However, the structure is not the one in which the permanent magnet is set inside a rotor, but it is the one in which the cylindrical permanent magnet 82 is stuck to the surface of the shaft 86 with an adhesive, that is so called xe2x80x9ca surface permanent magnet motorxe2x80x9d, namely that is the motor in which the permanent magnet 82 is just stuck to the shaft 86 with the adhesive.
The present invention aims to provide xe2x80x9can interior permanent magnet motorxe2x80x9d having a rotor which has permanent magnets stuck surely inside it so that the reliability is improved, and the rotor also has wide outer rotor rim space between the permanent magnets and the outer rotor rim edge for providing a wide magnetic flux path, still the travels of the magnetic flux into the adjacent magnets are suppressed, so that the efficiency is also improved.
Namely, the present invention provides a motor comprising a stator having a plurality of teeth provided with windings and a rotor including interior permanent magnets, then the rotor has a rotating shaft disposed at the center part, a rotor core fixed to the rotating shaft, permanent magnet slits formed inside the outer rim of the rotor, grooves formed at the walls of the slits, the magnets inserted into the slits, and adhesive layers inside the slits to stick the magnets to the rotor core.
With the structure described above, even if the size of the permanent magnet slits and the section size of the inserted permanent magnets are adjusted to be substantially same, the adhesive remains at least in the grooves, so that the magnets are surely stuck to the rotor core. Also in the present invention, by forming the portions of low magnetic induction at the outer rotor rim side comers of the permanent magnet slits, the travels of the magnetic flux into the adjacent magnets are suppressed, so that the efficient motor is realized.
By forming the grooves at the outer rotor rim side comers of the permanent magnet slits, and by filling up the grooves with the adhesive of low magnetic induction, the magnets are surely stuck to the rotor core and also the travels of the magnetic flux into the adjacent magnets are suppressed, which is extremely efficient.